I am including my ResourceDictionary files as Content files. Content files means they are not compiled or embedded, but they are loose files on disk.

One issue I need to solve was how to have the Design View in Expression Blend or Visual Studio.

It seems that Expression Blend has a partial solution but it doesn’t work in Visual Studio for me.

Steps for loading a ResourceDictionary from a loose file at design time

1. Locate your .proj file for your WPF Project.
2. Edit the .proj file with you favorite text editor.
   Note: I use Notepad++.
3. Find the ResourceDictionary file that is included as content.

       <Content Include="Resources\en-US\Common.View.LocalizationResources.en-US.xaml">
         <Generator>MSBuild:Compile</Generator>
         <SubType>Designer</SubType>
         <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
       </Content>
   

4. Change it to this:

       <Content Include="Resources\en-US\Common.View.LocalizationResources.en-US.xaml"
         Condition="'$(DesignTime)'=='true'
         OR ('$(SolutionPath)'!='' AND Exists('$(SolutionPath)')
         AND '$(BuildingInsideVisualStudio)'!='true'
         AND '$(BuildingInsideExpressionBlend)'!='true')">
         <Generator>MSBuild:Compile</Generator>
         <SubType>Designer</SubType>
         <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
       </Content>
   

5. Save and close the file.

Loading multiple ResourceDictionary files at design time

Sometimes Expression Blend will prompt you when it can’t find a resource and it will do this for you. However, it does something interesting.

It adds a file called DesignTimeResources.xaml in the Properties folder as a Page (not as Content).

    <Page Include="Properties\DesignTimeResources.xaml" 
      Condition="'$(DesignTime)'=='true' 
      OR ('$(SolutionPath)'!='' 
      AND Exists('$(SolutionPath)') AND '$(BuildingInsideVisualStudio)'!='true' 
      AND '$(BuildingInsideExpressionBlend)'!='true')">
      <Generator>MSBuild:Compile</Generator>
      <SubType>Designer</SubType>
      <ContainsDesignTimeResources>true</ContainsDesignTimeResources>
    </Page>

The file then looks as follows:

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <ResourceDictionary.MergedDictionaries>        
        <ResourceDictionary Source="E:\Dev\LD\Trunk\install\Common\LANDesk.Install.Common\Resources\en-US\Common.LocalizationResources.en-US.xaml"/>
    </ResourceDictionary.MergedDictionaries>
    <!-- Resource dictionary entries should be defined here. -->
</ResourceDictionary>

And then you can add more ResourceDictionaries without modifying the .proj file.

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <ResourceDictionary.MergedDictionaries>
        <ResourceDictionary Source="E:\Dev\LD\Trunk\install\SomeApp\Branding\StyleResources.xaml"/>
        <ResourceDictionary Source="E:\Dev\LD\Trunk\install\SomeApp\Branding\AlternateStyleResources.xaml"/>
        <ResourceDictionary Source="E:\Dev\LD\Trunk\install\SomeApp\Resources\en-US\en-US.xaml"/>
    </ResourceDictionary.MergedDictionaries>
    <!-- Resource dictionary entries should be defined here. -->
</ResourceDictionary>

ResourceDictionary with Relative Paths

Of course relative paths are more desired than static paths, especially when using projects among multiple people and from source control.

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <ResourceDictionary.MergedDictionaries>
        <ResourceDictionary Source="..\Branding\StyleResources.xaml"/>
        <ResourceDictionary Source="..\Branding\AlternateStyleResources.xaml"/>
        <ResourceDictionary Source="..\Resources\en-US\en-US.xaml"/>
    </ResourceDictionary.MergedDictionaries>
    <!-- Resource dictionary entries should be defined here. -->
</ResourceDictionary>

Resources:
http://www.tweened.org/en/2010/06/07/design-time-resources-dans-blend-4/